Rice disease management
Most rice diseases can be managed to minimize losses. The four most important strategies for rice disease management are to rotate crops, plant resistant varieties, plant in warm soil and use fungicides when necessary. An integrated approach that uses all of these methods is the most effective and profitable.
Resistant varieties: Varieties immune to all or most rice diseases do not exist. However, newer varieties often have improved levels of resistance. Growers should choose varieties based on MU yield trials in their area and resistance to locally important diseases.
Crop rotation: Rotating crops will help manage several rice diseases.
Planting in warm soil: Seedling rice diseases are accentuated when the soil around the seed and seedling is cool and wet. Seed and seedling death can result in severely reduced stands and consequent reduced yields. Growers should avoid planting in cool soil and when the weather forecast indicates that cool conditions may develop within several days of planting. Seed should be treated with a fungicide prior to planting.
Foliar fungicides: Scout rice fields for blast and sheath blight symptoms from internode elongation to 90% heading. If symptoms are found, prepare to use a foliar fungicide. Timing of foliar fungicide application to rice is essential for best disease control.
Additional information: An accurate diagnosis of plant disease is essential before selecting a management technique. Whenever possible, consult an expert in plant disease diagnosis. This guide is not intended to aid identification of rice diseases, but to be a rapidly accessible source of information on management techniques.
Other MU publications have more information on rice disease identification and management. They are:
These publications are available online and from the Delta Center, Missouri Agricultural Experiment Station, P.O. Box 160, Portageville, MO 63873. They also may be available at your local extension center.*
*These publications were made possible through the efforts of many others, including Joyce Elrod, senior research technician at the MU Delta Center.
|Disease and Pathogen||Symptoms||Remarks|
|Black sheath rot
|Dark brown-black discoloration from the crown up the stem. Leaves of heavily infected sheaths die. Tillering and yield may be reduced.||Usually only a problem in fields during the first few years rice is grown. Some cultivars are more susceptible than others.|
|Gray, football-shaped leaf lesions with brown margins. Leaf symptoms are rare. Nodes and panicles are darkened. When panicle infection occurs, heads will be white. The panicle may collapse.||Worse when rains occur frequently and temperatures are above 80 degrees F. Plant for a stand of 15 to 20 plants per square foot. Apply nitrogen at the time and rate recommended. Maintain flood to 4-inch depth. Avoid susceptible varieties. See MU publication MP 645.|
|Small oval to circular, brown leaf lesions. Infected heads are blackened. May be confused with kernel smut. Fingers will not be discolored when kernels are handled, as with kernel smut.||Occurs on plants stressed by low temperature, herbicide injury, other diseases and nitrogen deficiency. To control, prevent plant stress that may retard growth.|
|Infected kernels turn into a “smut ball.” It will first appear orange. Older smut balls are olive-green to brown and may be up to ½ inch across.||To minimize this disease:
|Minute, black masses of spores inside the hull burst the hull and are then visible. Hands are blackened by the spores when the kernels are handled.||Worse during warm, rainy weather at bloom. Apply recommended rates of nitrogen. Losses are seldom severe.|
Rhizoctonia, Pythium and Fusarium spp.
|Dead or weakened seedlings, discolored roots and thin stand.||Plant high-quality fungicide treated seed in a well-prepared seedbed. Plant for a stand of 15 to 20 plants per square foot.|
|Gray-green lesions with red-brown border near waterline. Lesions may be small at internode elongation and later extend up the stem.||Worse when humidity is high and temperatures are 90 degrees F. Yield loss can be severe. Plant for 15 to 20 plants per square foot. Plant least susceptible varieties. Follow recommended nitrogen rate and timing. See MU publication MP 646.|
|Similar to sheath blight, but symptoms are confined to the sheaths. Occurs in patches a few feet in diameter.||Occurs rarely. Avoid planting Lemont and Gulfmont in fields with a history of this problem. Application of fungicides may help.|
|Small black lesions on leaf sheath near waterline. Stems can be rotted and lodge. Dark gray mold and small black particles that resemble powdered charcoal can be seen inside stems.||Apply proper rates of potash and nitrogen. Avoid highly susceptible varieties.|
Issued in furtherance of Cooperative Extension Work Acts of May 8 and June 30, 1914, in cooperation with the United States Department of Agriculture. Ronald J. Turner, Director, Cooperative Extension Service, University of Missouri and Lincoln University, Columbia, Missouri 65211.